1. Field of the Invention
This invention relates to earth and rock boring apparatus, finding particular utility in the formation of vertical shafts to mines or other subterranean installations.
2. Statement of the Prior Art
It has been previously known to provide a plurality of drills supported in a casing within a housing pipe and to rotate both the support and pipes while the drills are free to rotate about their axis. Representative of patented art is U.S. Pat. No. 3,945,445.